Spectral Line Formation in NonLTE Expanding Atmospheres
Abstract
Summary. The local transfer equation is formulated for an optically thick atmosphere in which a linear velocity field is present, in order to obtain an integral equation for the line source function. The study and solution of this equation compared with that for the "static case" makes clear the effect of the shift of the absorption coefficient, due to the velocity gradient, upon the photons emitted in the line, in the continuum, and coming from the exterior (incident intensity). In some cases, the line source function in presence of a velocity gradient can be greater than in the "static case". The variation of emergent intensity with direction is greater than in the "static case"; consequently the geometric effect produced on the flux by this variation is very important. Emergent intensities and fluxes have also been computed. Some calculated lineprofiles have the shape of "P Cygni" or "Wolf Rayet" profiles. On the other hand, we have produced quasisymmetrical lineprofiles, which can be erroneously attributed to "micro turbulence" or rotational broadening. Key words: spectral line formation  moving atmospheres  radiative transfer
 Publication:

Astronomy and Astrophysics
 Pub Date:
 December 1973
 Bibcode:
 1973A&A....29..357S